Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 28 Oct 2019 19:14:19 -0700
From:   Andi Kleen <ak@linux.intel.com>
To:     Jiri Olsa <jolsa@redhat.com>
Cc:     Andi Kleen <andi@firstfloor.org>, acme@kernel.org,
        jolsa@kernel.org, eranian@google.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/7] perf pmu: Use file system cache to optimize sysfs
 access
Message-ID: <20191029021419.GT4660@tassilo.jf.intel.com>
References: <20191025181417.10670-1-andi@firstfloor.org>
 <20191025181417.10670-2-andi@firstfloor.org>
 <20191028220137.GF28772@krava>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20191028220137.GF28772@krava>
User-Agent: Mutt/1.12.1 (2019-06-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Oct 28, 2019 at 11:01:37PM +0100, Jiri Olsa wrote:
> On Fri, Oct 25, 2019 at 11:14:11AM -0700, Andi Kleen wrote:
> 
> SNIP
> 
> >  	if (pmu_aliases_parse(path, head))
> >  		return -1;
> > @@ -525,7 +524,6 @@ static int pmu_alias_terms(struct perf_pmu_alias *alias,
> >   */
> >  static int pmu_type(const char *name, __u32 *type)
> >  {
> > -	struct stat st;
> >  	char path[PATH_MAX];
> >  	FILE *file;
> >  	int ret = 0;
> > @@ -537,7 +535,7 @@ static int pmu_type(const char *name, __u32 *type)
> >  	snprintf(path, PATH_MAX,
> >  		 "%s" EVENT_SOURCE_DEVICE_PATH "%s/type", sysfs, name);
> >  
> > -	if (stat(path, &st) < 0)
> > +	if (access(path, R_OK) < 0)
> 
> why not file_available call in here?

iirc it doesn't do any redundant accesses.

-Andi